In the past 25 years, the detrimental effects of CO2 emissions have been realized. However, nearly 29 billion tons of CO2 are still released into the atmosphere each year (P. Friedlingstein et al., Nat. Geosci., 2010, 3, 811-812.) 6 billion tons are released in the US alone (see U.S. Greenhouse Gas Inventory Report: 1990-2013. EPA 430-R-15-004. Apr. 15, 2015; and see also the world wide web at epa.goviclimatechange/ghgemissions/usinventoryreport.html). Much of this comes from point sources of CO2 such as power plants, automobiles and the cement industry.
There are several known technologies that can capture CO2 from gas streams, including metal organic frameworks, membrane-based systems, and liquid capture, but the additional energy cost for their removal of CO2 hinders their application for commercial CO2 treatment. (R. P. Lively et al., Ind. Eng. Chem. Res., 2009, 48, 7314-7324; D. Camper et al., Ind. Eng. Chem. Res., 2008, 47, 8496-8498; H. Li, et al., Nature, 1999, 402, 276-279; H. J. Herog, Environ. Sci. Technol., 2001, 35, 148A-153A; D. M. D'Alessandro et al., Angew. Chem., Int. Ed., 2010, 49, 6058-6082: A. Oyenekan and G. T. Rochelle, Ind. Eng. Chem. Res., 2006, 45, 2457-2464; and S. Freguia and G. T. Rochelle, AIChE J., 2003, 49, 1676-1686.)
For example, in liquid capture approaches, such as aqueous monoethanolamine (MEA), the additional energy cost is the result of the heat capacity of water (4.18 J g−1K−1), the regeneration temperature (up to 120° C.) and the chemical bond energy between MEA and CO2 (83 kJ mol−1) (A. Oyenekan and G. T. Rochelle, Ind. Eng. Chem. Res., 2006, 45, 2457-2464; and S. Freguia and G. T. Rochelle, AIChE J., 2003, 49, 1676-1686.)
Accordingly, there exists a need to develop a method and apparatus to remove CO2 from gas streams that lowers the energy of capture and regeneration, or that harnesses alternative energy sources.